Bitcoin Core is very inconvenient to use compared to the lightweight Electrum wallet.
Wrong. Bitcoin Core is easy to use. It does exactly what you expect it to do.
Bitcoin Core doesn't even support SegWit
Wrong. I've been using Segwit addresses on Bitcoin Core for years.
this fact amazed me! That is, by using Bitcoin Core, users lose their money due to higher fees.
Wrong. Your "fact" is not a fact. Bitcoin Core transaction fees don't have to be higher than in Electrum.
At the same time, it cannot be said that Bitcoin Core is more secure than Electrum - it is not.
Just like it can't be said Electrum si more secure than Bitcoin Core. It depends on the user.
However, it is certainly much more difficult to use and requires very large computer resources.
Wrong. Bitcoin Core is more resource intensive than Electrum, but given current computing power, I wouldn't call it "very large".
Even though I'd generally recommend newbies to use Electrum instead of Bitcoin Core, both have their uses. Electrum for instance will become difficult to use when you've made 10,000 transactions.